A-ring reduction enhances the antigonadotropic potency of norethisterone

Potential of norethisterone enanthate for male contraception: pharmacokinetics and suppression of pituitary and gonadal function

OBJECTIVE

Gestagens are known to suppress gonadotrophins in women and are currently also under investigation for the development of hormonal male contraceptives. The aim of the study was to assess the potential of norethisterone enanthate (NETE) for male contraception.

DESIGN AND MEASUREMENTS

The suppressive effect of a single injection of 200 mg NETE on serum gonadotrophins, serum testosterone, lipids, spermatogenesis, well-being and sexual function was evaluated in seven healthy men.

RESULTS

In this single dose study treatment was well tolerated by all volunteers. NETE led to a rapid, profound and significant suppression of serum LH (day 6 - day 10), FSH (day 2 - day 29), testosterone (day 1 - day 29 and day 35) and SHBG (day 6 - day 35). At study end sperm counts were significantly suppressed. Numbers of spontaneous erections (day 17, 23 and 26), number of sexual fantasies (day 20 and 23) as well as libido (day 20 and 26) were significantly decreased compared to baseline. All other parameters including lipids, augmented glucose, testicular volume and well-being showed no significant alterations.

CONCLUSION

Because of its strong, rapid and sustained suppression of serum FSH and testosterone norethisterone enanthate offers great potential for hormonal male contraception if combined with testosterone esters.

Induction of male sexual behavior by norethisterone: role of its A-ring reduced metabolites

The estrogenic and androgenic potencies of norethisterone (NET), a synthetic nonaromatizable progestin, and three of its reduced metabolites (5 alpha-NET; 3 alpha, 5 alpha-NET; 3 beta, 5 alpha-NET) were assessed by their ability to restore male sexual behavior in castrated male rats following their chronic administration in combination with either 5 alpha-dihydrotestosterone (DHT) or estradiol (E2), or when given alone. Full restoration of mating was achieved when 3 beta, 5 alpha-NET was administered with DHT, indicating an estrogenic effect of this compound. Lower estrogenic effects were noticed with 3 alpha, 5 alpha-NET and 5 alpha-NET, while NET had very little estrogenic potency. The only effective compound to restore ejaculation, when administered with E2, was NET, indicating its androgen-like intrinsic potency. When administered alone, NET exerted the most potent effect on male behavior, followed by 5 alpha-NET, while the tetrahydro derivatives were ineffective. The observation that NET alone restored male sexual activity at a level identical to that induced by testosterone demonstrated an androgenic-estrogenic activity of this progestin exerted through its intrinsic androgenic effect, and the estrogenic effect of its tetrahydro derivatives. Overall results indicated that the metabolism of NET modulates its mode of action at the brain, and support the concept that both estrogenic and androgenic effects are required for mating activation.

Blood flow, substrate utilization and heat generation in tissues drained by the azygos vein in man

The present study was undertaken to examine the blood flow, heat generation and substrate utilization in tissues drained by the azygos vein in healthy subjects. Catheters were inserted percutaneously into the azygos vein and the pulmonary artery in 10 healthy male subjects in the basal, post-absorptive state. Blood flow in the azygos vein was measured by thermodilution technique, blood temperature was recorded in both the azygos vein and the pulmonary artery and blood samples for the determination of oxygen content and substrate concentrations were collected from both vessels repeatedly at timed intervals. Free fatty acid (FFA) exchange was evaluated following the intravenous infusion of 14-C labelled oleic acid. The average azygos vein blood flow was 94 +/- 10 ml/min. The coefficient of variation for the flow determination was 3.6%. The blood temperature in the azygos vein was consistently higher than that in the pulmonary artery, indicating an average calculated net heat production in the tissues of 0.5 W. The oxygen uptake to the tissues drained by the azygos vein amounted to 6 +/- 1 ml/min. Significant amounts of glucose, FFA and ketone bodies were taken up in the azygos area, while both glycerol and FFA were released. The FFA uptake could, if oxidized, account for about half of the oxygen uptake. In conclusion, the findings indicate that, in the basal state, the tissues drained by the azygos vein utilize both glucose and FFA. Heat is generated within the area but the rate of generation is low and can largely be explained by the oxidative metabolism. The findings do not support an important role for brown adipose tissue metabolism in the interscapular region in man.